Speed up overzooming in tile-join

[e-n-f]

Make tile-join faster:

clip.cpp

• allow creating overzoomed tiles without compression, since tile-join will immediate decompress them
• allow creating overzoomed tiles from an mvt_tile instead of always decompressing from a protobuf
• speed up clipping by doing a quick reject by bounding box if possible

tests/ne_110m_ocean/join/joined.mbtiles.json

The change to the test fixture is just because some tiles now have their layers generated in a different sequence because uncompressed (overzoomed) tiles compare earlier than than compressed (direct from mbtiles) tiles.

tile-join.cpp

• Keep a cache of parent tiles instead of retrieving the parent tile each time to create an overzoomed tile from it
• Decode the parent tiles to mvt_tile instead of leaving them compressed until it is time to use them
• Remove the current tile reader from the reader queue before checking whether the next tile on the queue is for the same tile that is currently being handled, which allows the output queue to be processed at the appropriate time instead of leaving everything to be done accumulating in memory until all of the tiles have been read